This proposal addresses the role of estrogens in regulating the early events in pregnancy. It will provide basic information on two aspects of human fertility: (1) embryonic mortality in early pregnancy is common in humans and mammals in general and (2) information is needed to design new approaches for fertility regulation. An understanding of the events of early pregnancy are important for solving these problems. Our long term objectives are to determine the autocrine and paracrine regulation functioning to promote the survival of the conceptus in early pregnancy. Specifically we wish to understand the mechanisms by which estrogens and catechol estrogens affect synthesis of prostaglandins and other arachidonic acid products. These products are linked to several changes in the embryo and uterus (i.e. vascular changes, implantation, embryonic development) that are required for pregnancy establishment. We are studying these mechanisms in the pig because the pig uterus and blastocyst provide relatively abundant amounts of tissue for biochemical studies and because enough is known about the synthesis of estrogens by pig blastocysts and about pig embryology, to design meaningful studies of biochemical mechanisms. Our approach is to study the cells of the endometrium in vitro for the ability of estrogens and catechol estrogens to modify the pattern of arachidonic acid metabolism. We will determine whether regulation occurs by release of substrate from phospholipids or by modifying the subsequent steps in the cyclooxygenase and lipoxygenase pathways. Further, we will determine the localization of catechol estrogen synthesis and of the enzyme, catechol-O-methyl transferase (COMT), in the luminal epithelium, glandular epithelium and stromal cells of the endometrium during early pregnancy. That information will allow evaluation of the potential for cell specific localization of catechol estrogen synthesis and COMT to modulate estrogen effects in the endometrium. Methods used to accomplish these aims are cell culture, HPLC to quantify the arachidonic acid products, radioimmunoassay of prostaglandins, and assay of COMT activity and catechol estrogen synthetic activity.